Lunhua 論畫, also called Moxie yaofa 模寫要法 or Motuo yaofa 摹拓要法, is a theory of painting compiled during the Eastern Jin period 東晉 (317-420) by the famous artist Gu Kaizhi 顧愷之 (c. 348-405).
The brief text is dedicated to the skill of transmitting and copying (linmo 臨摹) ancient artworks, as well as to the basic knowledge of painting. It describes how to select appropriate silk canvas, to use of brushes, and the application of strokes. Gu's book thus joins theoretical with practical skills. He holds that "copying" was not like to paint a gourd according to a model (yi yang hua hulu 依樣畫葫蘆), but the painter had, according to his experience of life, to transpose his thoughts to achieve extraordinary results (qian xiang miao de 遷想妙得), and also had to study theories of painting, methods of painting, contents of painting, and the characteristics of art. With the help of shapes, the painter had to describe the "spirit (of objects)" (yi xing xie shen 以形寫神), and had to become conscious of the union between objects and their spirit (wu dui tong shen 悟對通神). Gu Kaizhi believed that persons were most difficult to paint, followed by landscapes, animals, and buildings. The painter had to observe the right relationship between upper and lower, larger and smaller, extended and dense in order to preserve spirit and energy (shenqi 神氣) of things.
The original book is lost, but (part) of the text is preserved in Zhang Yanyuan's 張彥遠 (mid-9th cent.) Lidai minghua ji 歷代名畫記, where the text is composed of the two parts Lunhua 論畫, and Wei-Jin shengliu huazan 魏晉勝流畫贊, the former more theoretical, and the latter concerned with practice. Yu Jianhua 俞劍華 (1895-1979) criticized in his book Zhongguo hualun leibian 中國畫論類編 that the Lidai minghua ji erroneously mixed Gu's first chapter, Jin-Wei sheng liu huazan, with the title of his book, while the actual title of the first chapter was wrongly exchanged with that of the chapter Motuo yaofa 摹拓要法.